All About Bypass Capacitors

Bypass capacitors exist in almost every electronic device as they are crucial in keeping systems in good working order. 

Most electrical technicians and engineers understand this. Therefore, circuits, systems, and individual chips need bypassing for devices to function. 

Technicians usually place bypass capacitors between a DC signal and the ground as it removes any alternating current component of the signal.

 It also creates an alternating current short circuit to the ground. 

In essence, bypass capacitors act as the first line of defense. They dampen undesirable noise in your power supply. Integrated circuits lacking a bypass capacitor often have problems. 

Therefore, it’s the same for circuits with improper capacitors. It can cause severe power disturbances. 

Sometimes, those disturbances may lead to circuit failure. That’s why it is essential to understand the role of bypass capacitors, how they work, and how to configure them. 

Here’s an overview of bypass capacitors, their function, and their variants for different types of circuits. 

Table of Contents

What Is a Bypass Capacitor?

In electronics, a capacitor is a device that stores electric energy. Each one has two terminals, which work in tandem to produce an effect called capacitance. Capacitors have two metal plates that conduct electricity.

Between these plates is a dielectric material that acts as a conductor. This conductor may come in metal plates, thin foil, or electrodes

Electricity cord with electricity sparks 

Electricity cord with electricity sparks 

The dielectric medium increases the capacitance of the device. Again, this improves its ability to collect and store electrical energy. How does that happen?

The capacitor shorts the AC (alternating current) into the ground. As a result, it removes the AC noise on the DC signals.

A bypass capacitor produces proper DC (direct current) signals. It does this by shorting the AC (alternating current) into the ground, allowing you to remove the AC noise on the DC signals.

In other words, they “bypass” the AC noise and create a clear DC signal. Aside from reducing noise generated by the power supply, bypass capacitors can also direct electricity to any integrated circuits that need ample energy supplies.

Sometimes technicians call bypass capacitors decoupling capacitors. The two devices perform similar functions, though in different ways. But there is one main difference.

Bypass capacitors only need one unit to function. Decouplers need two different types of capacitors to work. 

What Are the Types of Bypass Capacitors?

Emitter Bypass Capacitor

An emitter capacitor is a capacitor connected in the Common-Emitter configuration. Its purpose is to prevent voltage gain drop.

Adding an emitter resistance to a Common Emitter (CE) amplifier reduces voltage gain while increasing the input impedance. 

Every time the bypass capacitor gets connected with an emitter resistance, it increases the voltage gain of the CE amplifier.

If you remove the capacitor, it produces severe degeneration in the amplifier circuit. As a result, the voltage gain reduces.  

Cathode Bypass Capacitor

Cathode bypass capacitors or “caps” feature prominently in amplifier circuits. Electronic technicians use them to control noise, gain, and frequency response.

Caps get rid of negative feedback. Therefore, they can work as open circuits for direct current (DC), allowing them to maintain the DC grid bias.  

Dual timing circuit operational amplifier

Dual timing circuit operational amplifier

Bypass Capacitor Size

The size of a bypass capacitor influences many things, like its ability to supply direct current to the device when needed. It also affects signal quality. Therefore, the basis of bypass capacitor sizing is the capacitance value

You must consider two factors when choosing the size of a capacitor. The current amount needed when switching a pin from low to high is the first thing to consider.

The second factor is the Maximum Pulse Slew Rate. It calculates the maximum current of the capacitor. 

What Are the Functions of Bypass Capacitors?

The primary function of a bypass capacitor is to bypass AC signals to the ground to produce cleaner DC signals. They cut voltage drops in the circuit by storing electric charges.

These charges get released when voltage spikes occur. Nearly all devices, both digital and analog, have bypass capacitors. Electronic technicians place the capacitor right next to the power pins. They’re also used in power supply sources.

All active devices in a circuit must use bypass capacitors near their power supply pins. Let’s say you have more than one bypass capacitor in the circuit.

The one with a smaller capacity gets placed close to the device.

In analog circuits, it’s different. Bypass capacitors redirect the high-frequency signals from the power supply into the ground.

It prevents signals from getting channeled into the sensitive analog IC through the power supply pin. Bypass capacitors decrease the likelihood of noise getting into the signal path in analog circuits. 

Closeup view of electronic circuit board 

Closeup view of the electronic circuit board 

What Are the Applications of Bypass Capacitors?

Bypass capacitors have three main applications. 

Filtering Power Supply

Technicians use large bypass capacitors to filter out the ripples in rectified sine waves. 

Meeting Current Demands

Bypass capacitors can provide the required current whenever a particular device needs it. For example, the drive current sent to a loudspeaker from an amplifier may vary according to the signal strength.

Also, the current demands of the amplifier’s output depending on how loud the signal is.

These variations in current at the output can lead to a varying current getting drained from the supply. Finally, the circuit experiences fluctuations sometimes coupled to the signal line.

These fluctuations manifest as noise through the power supply. Bypass capacitors help reduce these fluctuations, acting as temporary current sources in the circuit.

Maintaining Power Supply

In digital circuits, a bypass capacitor gets placed between the Common Collector Voltage (VCC) and the ground (GND) pins of all the integrated circuits (IC).

It maintains a steady power supply within the integrated circuit’s recommended range. It also stops high-frequency signals from entering the power supply.

Therefore, bypass capacitors also serve as immediate current providers in circuits with fast-switching. 

Where Should a Bypass Capacitor Be Placed?

The placement of bypass capacitors depends on several factors. It would help if you considered the board layout and size, the number of PCB layers, and the chip or component function.

Furthermore, each PCB has unique requirements. Placing the capacitor in the wrong place will cause mechanical problems or lead to circuit failures. 

For the best performance, electrical technicians recommend you place bypass capacitors as close to the supply pin of the component as possible.

This way, you reduce the impact of energy spikes during switching. Placing a bypass capacitor close to the supply pin of the component also gives it a low-impedance path to ground for AC noise signals. 


What Is the Other Name for a Bypass Capacitor?

Bypass capacitors also go by the name “decoupling capacitors.” Sometimes they’re referred to as bypass condensers. 

What Happens When You Remove a Bypass Capacitor?

Removing a bypass capacitor, you get extensive degeneration in the amplifier circuit. It also reduces the voltage gain. 

Board of an amplifier

Board of an amplifier

What’s the Difference Between a Bypass Capacitor and a Coupling Capacitor?

Bypass capacitors provide a low-impedance path at the frequency, channeling AC signals to the ground. Coupling capacitors, also known as DC-blocking capacitors, send alternating current signals from one node to another. 


Now you’ve gained some insights about bypass capacitors and their importance in electrical equipment.

Suppose you are an IT or DIY enthusiast. This information will benefit your projects, mainly when repairing electrical or mechanical issues in printed circuit boards. 

It may seem complex initially, but with practice, research, and familiarity, you’ll quickly figure out how to calibrate bypass capacitors to serve your needs.

A bypass capacitor is essential, whether for audio correction, power factor correction, voltage references, or signal coupling and decoupling.

Therefore, you’ll end unwanted noise, avoid power surges or shorts, and ensure your circuit produces the cleanest DC signals.